Transcript network - Piazza

CS450 – Introduction to Networking
Final review
Phu Phung
April 29, 2015
Internet protocol stack
•
application: supporting network
applications
– FTP, SMTP, HTTP
•
transport: process-process data
transfer
– TCP, UDP
•
network: routing of datagrams
from source to destination
application
transport
network
– IP, routing protocols
•
link: data transfer between
neighboring network elements
– Ethernet, 802.111 (WiFi), PPP
•
physical: bits “on the wire”
link
physical
A must remember diagram
HTTP connections
non-persistent HTTP
persistent HTTP
• at most one object sent • multiple objects can
over TCP connection
be sent over single
TCP connection
– connection then
between client, server
closed
• downloading multiple
objects required
multiple connections
DNS: services, structure
DNS services
• hostname to IP address
translation
• host aliasing
– canonical, alias names
• mail server aliasing
• load distribution
– replicated Web servers:
many IP addresses
correspond to one
name
Internet transport-layer protocols
• reliable, in-order
delivery (TCP)
– congestion control
– flow control
– connection setup
• unreliable, unordered
delivery: UDP
– no-frills extension of
“best-effort” IP
• services not available:
– delay guarantees
– bandwidth guarantees
application
transport
network
data link
physical
network
data link
physical
network
data link
physical
network
data link
physical
network
data link
physical
network
data link
physical
network
data link
physical
network
data link
physical
application
transport
network
data link
physical
Addressing processes
• identifier includes both IP
address and port numbers
associated with process on
host.
• example port numbers:
– HTTP server: 80
– mail server: 25
• to send HTTP message to
www.cs.uic.edu web server:
– IP address: 131.193.32.29
– port number: 80
• more shortly…
Network layer
• transport segment from
sending to receiving host
• on sending side encapsulates
segments into datagrams
• on receiving side, delivers
segments to transport layer
• network layer protocols in
every host, router
• router examines header
fields in all IP datagrams
passing through it
application
transport
network
data link
physical
network
data link
physical
network
data link
physical
network
data link
physical
network
data link
physical
network
data link
physical
network
data link
physical
network
data link
physical
network
data link
physical
network
data link
physical
network
data link
physical
network
data link
physical
application
transport
network
data link
physical
Two key network-layer functions
• forwarding: move
packets from
router’s input to
appropriate router
output
• routing: determine
route taken by
packets from source
to dest.
– routing algorithms
analogy:


routing: process of
planning trip from source
to dest
forwarding: process of
getting through single
interchange
Router architecture overview
two key router functions:
•
•
run routing algorithms/protocol (RIP, OSPF, BGP)
forwarding datagrams from incoming to outgoing link
forwarding tables computed,
pushed to input ports
routing
processor
routing, management
control plane (software)
forwarding data
plane (hardware)
high-seed
switching
fabric
router input ports
router output ports
Routing: Comparison of LS and DV algorithms
message complexity
• LS: with n nodes, E links, O(nE)
msgs sent
• DV: exchange between neighbors
only
– convergence time varies
speed of convergence
• LS: O(n2) algorithm requires
O(nE) msgs
– may have oscillations
• DV: convergence time varies
– may be routing loops
– count-to-infinity problem
robustness: what happens if
router malfunctions?
LS:
– node can advertise incorrect
link cost
– each node computes only its
own table
DV:
– DV node can advertise
incorrect path cost
– each node’s table used by
others
• error propagate thru
network
Hierarchical routing
our routing study thus far - idealization
 all routers identical
 network “flat”
… not true in practice
scale: with 600 million
destinations:
• can’t store all dest’s in
routing tables!
• routing table exchange
would swamp links!
administrative autonomy
• internet = network of
networks
• each network admin may
want to control routing in
its own network
Hierarchical routing
• aggregate routers into
regions, “autonomous
systems” (AS)
• routers in same AS run
same routing protocol
– “intra-AS” routing
protocol
– routers in different AS
can run different intra-AS
routing protocol
gateway router:
• at “edge” of its own AS
• has link to router in
another AS
IP addressing
• IP address: 32-bit
223.1.1.1
identifier for host, router
223.1.1.2
interface
• interface: connection
between host/router and
physical link
223.1.2.1
223.1.1.4
223.1.3.27
223.1.1.3
223.1.2.2
– router’s typically have
multiple interfaces
– host typically has one or
two interfaces (e.g., wired
Ethernet, wireless 802.11)
• IP addresses associated
with each interface
223.1.2.9
223.1.3.1
223.1.3.2
223.1.1.1 = 11011111 00000001 00000001 00000001
223
1
1
1
Subnets
• IP address:
–subnet part - high order
bits
–host part - low order
bits
• what’s a subnet ?
–device interfaces with
same subnet part of IP
address
–can physically reach
each other without
intervening router
223.1.1.1
223.1.1.2
223.1.1.4
223.1.2.1
223.1.2.9
223.1.2.2
223.1.1.3
223.1.3.27
subnet
223.1.3.1
223.1.3.2
network consisting of 3 subnets
IP addressing: CIDR
CIDR: Classless InterDomain Routing
– subnet portion of address of arbitrary length
– address format: a.b.c.d/x, where x is # bits in
subnet portion of address
subnet
part
host
part
11001000 00010111 00010000 00000000
200.23.16.0/23
DHCP client-server scenario
DHCP
server
223.1.1.0/24
223.1.2.1
223.1.1.1
223.1.1.2
223.1.1.4
223.1.1.3
223.1.2.9
223.1.3.27
223.1.2.2
223.1.2.0/24
223.1.3.2
223.1.3.1
223.1.3.0/24
arriving DHCP
client needs
address in this
network
NAT: network address translation
rest of
Internet
local network
(e.g., home network)
10.0.0/24
10.0.0.1
10.0.0.4
10.0.0.2
138.76.29.7
10.0.0.3
all datagrams leaving local
network have same single
source NAT IP address:
138.76.29.7,different source
port numbers
datagrams with source or
destination in this network
have 10.0.0/24 address for
source, destination (as usual)
IPv6
• initial motivation: 32-bit address space soon to
be completely allocated.
• additional motivation:
– header format helps speed processing/forwarding
– header changes to facilitate QoS
IPv6 datagram format:
– fixed-length 40 byte header
– no fragmentation allowed
Tunneling
IPv4 tunnel
connecting IPv6 routers
A
B
IPv6
IPv6
A
B
C
IPv6
IPv6
IPv4
logical view:
E
F
IPv6
IPv6
D
E
F
IPv4
IPv6
IPv6
physical view:
flow: X
src: A
dest: F
data
A-to-B:
IPv6
src:B
dest: E
src:B
dest: E
Flow: X
Src: A
Dest: F
Flow: X
Src: A
Dest: F
data
data
B-to-C:
IPv6 inside
IPv4
B-to-C:
IPv6 inside
IPv4
flow: X
src: A
dest: F
data
E-to-F:
IPv6
Where is the link layer implemented?
• in each and every host
• link layer implemented in
“adaptor” (aka network
interface card NIC) or on a chip
– Ethernet card, 802.11 card;
Ethernet chipset
– implements link, physical
layer
• attaches into host’s system
buses
• combination of hardware,
software, firmware
application
transport
network
link
cpu
memory
controller
link
physical
host
bus
(e.g., PCI)
physical
transmission
network adapter
card
Multiple access links, protocols
two types of “links”:
• point-to-point
– PPP for dial-up access
– point-to-point link between Ethernet switch, host
• broadcast (shared wire or medium)
– old-fashioned Ethernet
– upstream HFC
– 802.11 wireless LAN
shared wire (e.g.,
cabled Ethernet)
shared RF
(e.g., 802.11 WiFi)
shared RF
(satellite)
humans at a
cocktail party
(shared air, acoustical)
ARP: address resolution protocol
Question: how to determine
interface’s MAC address,
knowing its IP address?
137.196.7.78
1A-2F-BB-76-09-AD
137.196.7.23
137.196.7.14
LAN
71-65-F7-2B-08-53
58-23-D7-FA-20-B0
0C-C4-11-6F-E3-98
137.196.7.88
ARP table: each IP node (host,
router) on LAN has table
– IP/MAC address
mappings for some
LAN nodes:
< IP address; MAC address; TTL>
– TTL (Time To Live):
time after which
address mapping will
be forgotten (typically
20 min)
Ethernet switch
• link-layer device: takes an active role
– store, forward Ethernet frames
– examine incoming frame’s MAC address,
selectively forward frame to one-or-more
outgoing links when frame is to be forwarded on
segment, uses CSMA/CD to access segment
• transparent
– hosts are unaware of presence of switches
• plug-and-play, self-learning
– switches do not need to be configured
Switches vs. routers
both are store-and-forward:
 routers: network-layer
devices (examine networklayer headers)
 switches: link-layer devices
(examine link-layer
headers)
both have forwarding tables:
 routers: compute tables
using routing algorithms, IP
addresses
 switches: learn forwarding
table using flooding,
learning, MAC addresses
datagram
frame
application
transport
network
link
physical
frame
link
physical
switch
network datagram
link
frame
physical
application
transport
network
link
physical
VLANs: motivation
consider:
• CS user moves office to EE, but
wants connect to CS switch?
• single broadcast domain:
Computer
Science
Electrical
Engineering
Computer
Engineering
– all layer-2 broadcast
traffic (ARP, DHCP,
unknown location of
destination MAC
address) must cross
entire LAN
– security/privacy,
efficiency issues
802.11 LAN architecture

Internet
wireless host
communicates with base
station
 base station = access point
(AP)
hub, switch
or router

Basic Service Set (BSS) (aka
“cell”) in infrastructure
mode contains:
 wireless hosts
 access point (AP): base
station
 ad hoc mode: hosts only
BSS 1
BSS 2
802.11: Channels, association
• 802.11b: 2.4GHz-2.485GHz spectrum divided into 11 channels at
different frequencies
– AP admin chooses frequency for AP
– interference possible: channel can be same as that
chosen by neighboring AP!
• host: must associate with an AP
– scans channels, listening for beacon frames containing
AP’s name (SSID) and MAC address
– selects AP to associate with
– may perform authentication [Chapter 8]
– will typically run DHCP to get IP address in AP’s
subnet
HTTPS Transaction
Client Browser
TCP
Connect
SSL
Connect
HTTPS GET
transaction
Web Server
A day in the life: scenario
DNS server
browser
Comcast network
68.80.0.0/13
school network
68.80.2.0/24
web page
web server
64.233.169.105
Google’s network
64.233.160.0/19
Grade weighting
Final Exam: 1-3PM
Monday May 4, 2015 in SES 238
• 35 points (+ 5 additional bonus points)
• One handwriting letter sheet of notes
• Content
– Everything in the lectures 
• Grades (A, B, C …) are curved based on an
aggregate course score
– average score is calculated without bonus points
Final words
• Study hard and good luck to the exam
• Exam: 1-3PM Monday May 4, 2015 in this
room
• Thank you for your participation, good luck to
your future.
• Complete the course evaluation
• Email or visit me if you have
questions/comments on the course, or job
interviews related, or …